The present invention relates to a sheet feed mechanism, and more particularly to a sheet feed mechanism for use in a device for applying a laser beam to a scanned member such as a stimulable phosphor sheet, for example, to read an image recorded thereon, the sheet feed mechanism including a pair of rollers movable into curved passage for delivering the scanned member therethrough after the image has been read from the scanned member, the rollers being retracted from the passage away from each other while the image is being read from the scanned member, so that precise image information can be reproduced without imposing unwanted shocks on the scanned member during the image reading process, the sheet feed mechanism being arranged to reduce the size of the device.
There has recently been developed and widely used a radiation image recording and reproducing system for producing the radiation-transmitted image of an object using a stimulable phosphor material capable of emitting light upon exposure to stimulating rays. When a certain phosphor is exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, the phosphor stores a part of the energy of the radiation. When the phosphor exposed to the radiation is subsequently exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the stored energy of the radiation. The phosphor exhibiting such a property is referred to as a "stimulable phosphor".
In the radiation image recording and reproducing system employing such a stimulable phosphor, the radiation image information of an object such as a human body is stored in a sheet having a layer of stimulable phosphor, and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected to produce an image information signal that is electrically processed for generating image information which is recorded as a visible image on a recording medium such as a photosensitive material or displayed as a visible image on a CRT or the like.
The radiation image recording and reproducing system includes an image reading device for reading the radiation image recorded on a stimulable phosphor sheet. The image reading device reads the radiation image as follows:
The stimulable phosphor sheet is two-dimensionally scanned by a light beam such as a laser beam, and light emitted from the stimulable phosphor sheet in response to application of the light beam is detected in time series by a light detector such as a photomultiplier or the like, for thereby obtaining image information. The two-dimensional scanning of the stimulable phosphor sheet with the light beam is effected by mechanially feeding the stimulable phosphor sheet in one direction with a belt conveyor or the like for auxiliary scanning, while deflecting the light beam for main scanning in a direction normal to the direction in which the stimulable phosphor sheet is fed.
The image information thus obtained is sent to an image recorder. In the image recorder, a photographic photosensitive material serving as a recording material is exposed to a laser beam modulated by the image information produced from the stimulable phosphor sheet for recording an image on the photographic photosensitive material. The photographic photosensitive material with the image recorded thereon is then transferred to an image developing device and processed thereby to develop the image. The photographic photosensitive material is thereafter stored in a prescribed place for use in medical diagnosis when required.
Stimulable phosphor sheets of different sizes are used to meet various needs or applications. If stimulable phosphor sheets are to be fed stably and smoothly in the image reading device from the time when the image starts being read to the time when the image reading is finished, then a feed path of a length which is about twice the length of the maximum-size sheet. As a result, the image reading device takes up a large installation space.
One solution to the above drawback is to have a sheet feed passage curved upwardly. The curved sheet feed passage requires a plurality of drive roller pairs spaced as feed sources at intervals therealong which should be smaller than the length of stimulable phosphor sheets of a minimum size.
While a stimulable phosphor sheet is being scanned to read the image recorded thereon, the leading end, which has been scanned, of the sheet is shocked when it is gripped by a pair of drive rollers disposed in the curved sheet feed passage. The shock thus applied to the stimulable phosphor sheet tends to adversely affect the scanning process for the remaining portion of the sheet. More specifically, when the stimulable phosphor sheet being scanned is accidentally displaced by a shock, no accurate image can therafter be read from the sheet, and no desired radiation image information can be reproduced. If inaccurate image information is used for medical diagnosis, a diagnostic error may be caused.